693 research outputs found

    Dynamical Dark Energy and Spontaneously Generated Gravity

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    We study the cosmological evolution of an induced gravity model with a scale symmetry breaking potential for the scalar field. The radiation to matter transition, following inflation and reheating, influences the dynamics of such a field through its non minimal coupling. We illustrate how, under certain conditions on the potential, such a dynamics can lead to a suitable amount of dark energy explaining the present accelerated expansion.Comment: 14 pages, 3 figure

    Scaling attractors for quintessence in flat universe with cosmological term

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    For evolution of flat universe, we classify late time and future attractors with scaling behavior of scalar field quintessence in the case of potential, which, at definite values of its parameters and initial data, corresponds to exact scaling in the presence of cosmological constant.Comment: 11 pages, 16 eps-figures, revtex4, reference with comment adde

    Expansion history and f(R) modified gravity

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    We attempt to fit cosmological data using f(R)f(R) modified Lagrangians containing inverse powers of the Ricci scalar varied with respect to the metric. While we can fit the supernova data well, we confirm the at1/2a\propto t^{1/2} behaviour at medium to high redshifts reported elsewhere and argue that the easiest way to show that this class of models are inconsistent with the data is by considering the thickness of the last scattering surface. For the best fit parameters to the supernova data, the simplest 1/R model gives rise to a last scattering surface of thickness Δz530\Delta z\sim 530, inconsistent with observations.Comment: accepted in JCAP, presentation clarified, results and conclusions unchange